The present invention relates to electric switches, circuit breakers or current interrupters, and, more particularly, to a device for connecting a molded case electric circuit breaker to a stab terminal on an electric panelboard.
Several devices are currently utilized for connecting electric circuit breakers to electric panelboards. One common example is a plug-on connector, wherein the electrical connection is made by a resilient terminal clip having converging clamping arms that grip a stab terminal on a panelboard. In some constructions, a spring clip surrounds the terminal clip and enhances the connection. Typical plug-on connectors are disclosed in U.S. Pat. Nos. 4,020,400 and 3,383,486.
Plug-in connectors provide a convenient and space efficient means for connecting a circuit breaker to a panelboard; however, in some applications, a more conductive and sturdy connection is required. In addition, for certain applications, Underwriters Laboratories (UL) requires that circuit breakers using plug-in connectors be provided with an additional fastening means such that the circuit breaker requires more than a pull to release it from its mounted position on the panelboard.
In response to such requirements, some circuit breakers have been designed with a terminal lug which is secured to the panelboard terminal bus with a threaded fastener, such as a bolt or screw, to make the electrical connection between the circuit breaker and the panelboard. A device of this type is disclosed in FIG. 3 of U.S. Pat. No. 4,020,400. One disadvantage associated with the above-described bolt-on connection means is that additional space is required on the panelboard between rows of circuit breakers to provide access to the screws which fasten the terminal lug to the panelboard terminal bus. Such extra space increases material costs of the panelboard terminals, as well as the housings or enclosures therefor. Further disadvantages of circuit breakers having bolt-on lugs are that (1) such circuit breakers may only be installed on panelboards having terminals with appropriately sized threaded holes; (2) checking the tightness of the screw involves potential exposure to hazardous voltages; and (3) overtightening of the screw may damage the panelboard terminal.
Another prior art means of connecting electric circuit breakers to panelboards comprises a flexible bolt-on terminal tab adapted to be folded under the circuit breaker after the tab is secured to the panelboard terminal with a threaded fastener. U.S. Pat. No. 4,144,554 describes such an arrangement. With such flexible terminals, it is not necessary to leave a space between rows of circuit breakers. Although this device does not require as much space as the non-folding bolt-on terminal lugs, it is subject to the above-described disadvantages of bolt-on lug circuit breakers. Both the above-described prior art devices require the manufacture of differently constructed circuit breakers for the bolt-on and plug-in markets.
U.S. Pat. No. 3,538,390 describes a circuit breaker system having a terminal clip that may alternatively be used as a plug-in connector (FIG. 3) or as a bolt-on connector (FIG. 11). A disadvantage of such a system is that the circuit breaker terminal clip cannot be readily bolted to the panelboard terminal while it is being used as a plug-in connector. In order to function as a bolt-on connector, the circuit breaker terminal must be unbolted and removed from the circuit breaker and then bolted to the panelboard terminal and rebolted to the circuit breaker. As in the previously described bolt-on connectors, the panelboard terminal must be provided with a hole for the bolt, and checking the circuit breaker connection may involve a potentially hazardous exposure to high potentials.
All of the above-mentioned prior art devices are generally either not sufficiently secure for many applications, are not space efficient, or have other disadvantages as discussed above.